1. Field of the Invention
The present invention relates to a liquid discharging head for discharging a desired liquid by a novel discharge principle and, more particularly, to a liquid discharging head and a liquid discharging device having the structure for displacing a movable member by making use of generation of bubble.
The liquid discharging head of the present invention is the invention applicable to equipment such as a printer, a copying machine, a facsimile machine having a communication system, a word processor having a printer portion or the like, and an industrial recording device combined with one or more of various processing devices, with which recording is effected on a recording medium such as paper, thread, fiber, textile, leather, metal, plastic material, glass, wood, ceramic material, and so on.
It is noted here that xe2x80x9crecordingxe2x80x9d in the present invention means not only provision of an image having meaning, such as characters or graphics, on a recorded medium, but also provision of an image having no meaning, such as patterns, on the medium.
2. Related Background Art
One of the conventionally known recording methods is an ink jet recording method for imparting energy of heat or the like to ink so as to cause a state change accompanied by a quick volume change of ink (generation of bubble), thereby discharging the ink through a discharge opening by acting force based on this state change, and depositing the ink on a recorded medium, thereby forming an image, which is so called as a bubble jet recording method. A recording apparatus using this bubble jet recording method is normally provided, as disclosed in the specification of U.S. Pat. No. 4,723,129, with discharge openings for discharging the ink, ink flow paths in communication with the respective discharge openings, and electrothermal transducers as energy generating means for discharging the ink located in the ink flow path.
The above recording method permits high-quality images to be recorded at high speed and with low noise and in addition, because a head for carrying out this recording method can have the discharge openings for discharging the ink as disposed in high density, it has many advantages; for example, high-resolution recorded images or even color images can be obtained readily by compact apparatus. Therefore, this bubble jet recording method is used in many office devices including printers, copiers, facsimile machines, and so on in recent years and further is becoming to be used for industrial systems such as textile printing apparatus.
With spread of use of the bubble jet technology in products in wide fields, a variety of demands described below are increasing these years.
For example, an example of investigation to meet the demand to improve the energy use efficiency is optimization of the heat generating member such as adjustment of the thickness of a protecting film. This technique is effective to an improvement in transfer efficiency of generated heat into the liquid.
In order to provide high-quality images, proposed were driving conditions for realizing the liquid discharge method or the like capable of performing good ink discharge based on high-speed discharge of ink and stable generation of bubble. From the standpoint of high-speed recording, proposed was an improvement in a configuration of flow path in order to obtain a liquid discharging head with high filling (refilling) speed into the liquid flow path of the liquid discharged.
Among this configuration of liquid passage, the publication of Japanese Patent Application Laid-open No. 63-199972, for example, describes the flow passage structure as shown in FIGS. 22A and 22B. The flow passage structure and the head producing method described in this publication are of the invention accomplished noting the back wave occurring with generation of bubble (i.e., the pressure directed in the opposite direction to the direction toward the discharge opening, which is the pressure directed to a liquid chamber 12). This back wave is known as loss energy, because it is not energy directed in the discharge direction.
The invention shown in FIGS. 22A and 22B discloses a valve 10 located apart from a generation region of a bubble formed by a heat generating member 2 and on the opposite side to the discharge opening 11 with respect to the heat generating member 2.
In FIG. 22B, this valve 10 is illustrated as being produced by the producing method making use of a plate material or the like, having an initial position where it is stuck to the ceiling of the flow path 3, and dropping into the flow path 3 with generation of bubble. This invention is disclosed as the one for suppressing the energy losses by controlling a part of the aforementioned back wave by the valve 10.
However, as apparent from investigation on the case where a bubble is generated inside the flow path 3 as retaining the liquid to be discharged in this structure, it is seen that to regulate the part of the back wave by the valve 10 is not practical for discharge of liquid.
The back wave itself originally has no direct relation with discharge, as discussed previously. At the point when the back wave appears in the flow path 3, as shown in FIG. 22B, the pressure directly related to discharge out of the bubble is already ready to eject the liquid from the flow path 3. It is thus clear that to regulate the back wave, more accurately, to regulate the part thereof, cannot give a great effect on discharge.
In the bubble jet recording method, on the other hand, heating is repeated while the heat generating member is in contact with the ink, which forms deposits due to scorching of ink on the surface of the heat generating member. A large amount of the deposits could be formed depending upon the type of ink, which could result in unstable generation of bubble and which could make it difficult to eject the ink in good order. It has been desired to achieve a method for well discharging the liquid without changing the property of the liquid to be discharged even if the liquid to be discharged is the one easily deteriorated by heat or even if the liquid is the one not easy to achieve adequate generation of bubble.
From this viewpoint, another proposal was made to provide a method to employ different types of liquids, a liquid (bubble generation liquid) for generating a bubble by heat and a liquid (discharge liquid) to be discharged, arranged to transmit the pressure upon generation of bubble to the discharge liquid and to eject the discharge liquid thereby, for example as disclosed in Japanese Patent Applications Laid-open No. 61-69467 and No. 55-81172, U.S. Pat. No. 4,480,259, and so on. In these publications, the ink as the discharge liquid is perfectly separated from the bubble generation liquid by a flexible film of silicone rubber or the like so as to keep the discharge liquid from directly contacting the heat generating member, and the pressure upon generation of bubble in the bubble generation liquid is transferred to the discharge liquid through deformation of the flexible film. By this structure, the method achieved prevention of the deposits on the surface of the heat generating member, an improvement in freedom of selection of the discharge liquid, and so on.
However, with the head of this structure in which the discharge liquid and the bubble generation liquid are completely separated from each other as described above, since the pressure upon bubble generation is transferred to the discharge liquid through the expansion/contraction deformation of the flexible film, the pressure by generation of bubble is absorbed to a quite high degree by the flexible film. In addition, the deformation of the flexible film is not so large, and therefore, the energy use efficiency and the discharge force could be degraded, though it is possible to achieve the effect by the separation of the discharge liquid from the bubble generation liquid.
The major subject of the present invention is to enhance the fundamental discharge characteristics of the method for discharging the liquid by forming a basically conventional bubble (particularly, a bubble accompanying film boiling) in the liquid flow path to a level that has never been expected heretofore, from the viewpoint that has never been contemplated heretofore.
Returning to the principle of discharge of liquid droplet, some of the inventors have conducted extensive and intensive research to provide a novel liquid discharging method utilizing a bubble that has never been obtained heretofore, and a head used therein, and the like. At that time, they conducted a first technical analysis placing the starting point on the operation of the movable member in the liquid flow path to analyze the principle of the mechanism of movable member in the flow path, a second technical analysis placing the starting point on the liquid droplet discharge principle by the bubble, and a third analysis placing the starting point on the bubble forming region of the heat generating member for formation of bubble.
Based on these analyses, they have established the utterly novel technology for positively controlling the bubble by arranging the fulcrum and free end of the movable member in such a positional relation that the free end is located on the discharge opening side, that is, on the downstream side and by so arranging the movable member as to face the heat generating member or the bubble generation region.
Next, it was found that, considering the energy given to the discharge liquid by the bubble itself, a maximum factor to considerably improve the discharge properties was to take account of downstream growing components of the bubble. Namely, it was also clarified that the discharge efficiency and discharge rate were improved just by efficiently directing the downstream growing components of the bubble along the discharge direction. This led the present inventors to an extremely high technical level, as compared with the conventional technical level, that the downstream growing components of the bubble are positively moved to the free end side of the movable member.
Further, it was found that it was also preferred to take account of the structural elements such as the movable member, the liquid flow path, and so on related to the growth of bubble on the downstream side in the heat generation region for forming the bubble, for example, on the downstream side of the center line passing the center of the area of the electrothermal transducer in the direction of flow of liquid or on the downstream side of the center of the area of the surface contributing to the bubble generation.
It was further found that the refilling rate was able to be greatly improved taking account of the location of the movable member and the structure of the liquid supply passages.
Some of the inventors and the applicant have filed applications concerning excellent liquid discharge principles from the knowledge obtained by such research and the all-inclusive viewpoints, and the inventors have come to have a more preferred idea on the basis of this invention.
The point that the present inventors recognized is to provide a high-density liquid discharging head with furthermore stabilized discharge force, especially considering the positional relation between the heat generating member and the second liquid path in the present invention.
The main objects of the present invention are as follows.
A first object of the present invention is to provide a liquid discharging head and a liquid discharging device that can transmit growth of the generated bubble more intensively and efficiently to the upper side or to the discharge opening side by the positional relation between the bubble generation region and the heat generating member.
A second object of the present invention is to provide a liquid discharging head and a liquid discharging device that can largely decrease accumulation of heat in the liquid above the heat generating member as improving the discharge efficiency and discharge pressure and that can perform good liquid discharge by decreasing residual bubbles above the heat generating member.
A third object of the present invention is to provide a liquid discharging head and a liquid discharging device enhanced in refilling frequency and improved in print speed or the like by suppressing the action of inertial force in the opposite direction to the liquid supply direction due to the back wave and decreasing a meniscus back amount by a valve function of the movable member.
A fourth object of the present invention is to provide a liquid discharging head and a liquid discharging device that can reduce the deposits on the heat generating member, that can broaden the application range of the discharge liquid, and that can demonstrate considerably high discharge efficiency and discharge force.
A fifth object of the present invention is to provide a liquid discharging head and a liquid discharging device that can increase degrees of freedom of selection of the liquid to be discharged.
A sixth object of the present invention is to provide a liquid discharging head and a liquid discharging device permitting easy fabrication of the liquid discharging head as described above.
For achieving the above objects, the present invention provides a liquid discharging head comprising a discharge opening for discharging a liquid, a bubble generation region for generating a bubble by applying heat to the liquid by a heat generating member, and a movable member so positioned as to face the bubble generation region and arranged as displaceable between a first position and a second position more distant from the bubble generation region than the first position, the movable member being displaced from the first position to the second position by pressure based on generation of the bubble in the bubble generation region and the bubble being made to expand more downstream than upstream with respect to a direction toward the discharge opening by displacement of the movable member, thereby discharging the liquid, wherein in the heat generating member there exists a bubbling region involved in the generation of bubble, centers of widths of the heat generating member and an effective bubbling region with respect to a flow direction of the liquid are identical, and conditions of the bubble generation region are given as follows:
the width of the effective bubbling regionxe2x89xa6the width of the bubble generation regionxe2x89xa6the width of the heat generating member.
Also, the present invention is characterized in that in the above liquid discharging head, (the width of the heat generating member)xe2x88x928 xcexcmxe2x89xa6(the width of the bubble generation region).
Further, the present invention is characterized in that in the above liquid discharging head, when the flow direction of the liquid is along a direction of lengths of the heat generating member and the effective bubbling region, the conditions of the bubble generation region are given as follows: the length of the effective bubbling regionxe2x89xa6the length of the bubble generation regionxe2x89xa6the length of the heat generating member.
Also, the present invention is characterized in that in the above liquid discharging head, an area of the effective bubbling regionxe2x89xa6an area of the movable member and in a stationary state the movable member hermetically closes the effective bubbling region.
In the present invention, the bubble generated can be made to grow upward or to the discharge opening side by the feature of (the width of the effective bubbling regionxe2x89xa6the width of the bubble generation regionxe2x89xa6the width of the heat generating member). This can make the discharge force stabler. In addition, it becomes possible to achieve a higher density arrangement, thereby enabling to improve the quality of image.
In addition, the liquid discharging method, head, and so on according to the present invention, based on the very novel discharge principle, as described above, can attain the synergistic effect of the bubble generated and the movable member displaced thereby, so that the liquid near the discharge opening can be discharged efficiently, thereby improving the discharge efficiency as compared with the conventional discharge methods, heads, and so on of the bubble jet type. For example, the most preferable embodiment of the present invention achieved the breakthrough discharge efficiency two or more times improved.
With the further characteristic structure of the present invention, discharge failure can be prevented even after long-term storage at low temperature or at low humidity, or, even if discharge failure occurs, the head can be advantageously returned instantaneously into the normal condition only with a recovery process such as preliminary discharge or suction recovery.
Specifically, under the long-term storage condition to cause discharge failure of almost all of discharge openings in the head of the conventional bubble jet type having sixty four discharge openings, the head of the present invention showed discharge failure only in approximately half or less of the discharge openings. For recovering these heads by preliminary discharge, several thousand preliminary discharges were required for each discharge opening in the conventional head, whereas a hundred or so preliminary discharges were sufficient to recover the head of the present invention. This means that the present invention can shorten the recovery period, can decrease losses of the liquid due to recovery, and can greatly lower the running cost.
Particularly, the structure for improving the refilling characteristics according to the present invention achieved high responsivity upon continuous discharge, stable growth of bubble, and stabilization of liquid droplet and enabled high-speed recording or high-quality recording based on the high-speed liquid discharge.
The other effects of the present invention will be understood from the description of the embodiments.
The terms xe2x80x9cupstreamxe2x80x9d and xe2x80x9cdownstreamxe2x80x9d used in the description of the invention are defined with respect to the direction of general liquid flow from a liquid supply source through the bubble generation region (or the movable member) to the discharge opening or are expressed as expressions as to this structural direction.
Further, the xe2x80x9cdownstream sidexe2x80x9d of the bubble itself represents an discharge-opening-side portion of the bubble which directly functions mainly to eject a liquid droplet. More particularly, it means a downstream portion of the bubble in the above flow direction or in the above structural direction with respect to the center of the bubble, or a bubble appearing in the downstream region from the center of the area of the heat generating member.
A xe2x80x9csubstantially sealedxe2x80x9d state used in the description of the invention generally means a sealed state in such a degree that while a bubble grows, the bubble is kept from escaping through a gap (slit) around the movable member before displacement of the movable member.
The xe2x80x9cpartition wallxe2x80x9d stated in the invention may mean a wall (which may include the movable member) interposed to separate the region in direct fluid communication with the discharge opening from the bubble generation region in a wide sense and, more specifically, means a wall for separating the liquid flow path including the bubble generation region from the liquid flow path in direct fluid communication with the discharge opening, thereby preventing mixture of the liquids in the respective liquid flow paths, in a narrow sense.
Further, a xe2x80x9cfree end portionxe2x80x9d of the movable member stated in the invention means a portion including the free end, which is a downstream-side end of the movable member, and its neighboring regions, and also including regions near the downstream corners of the movable member.
Further, a xe2x80x9cfree end regionxe2x80x9d of the movable member stated in the present invention means the free end itself as being the downstream-side end of the movable member, a region near the free end, or a region including both the free end and the side edges.
In addition, xe2x80x9cresistance of liquid flow path against the movable memberxe2x80x9d stated in the present invention means a resistance that the liquid in the liquid flow path gives to the movable member while the movable member moves away from the bubble generation region with generation of bubble. Therefore, the present invention involves all technical contents directed to controlling the behavior of the movable member by changing the resistance, i.e., by forming a slope of resistance, by use of a resistance by a physical stopper, by use of a resistance by a substantial stopper with intervention of liquid, or the like. In the following description, this resistance will be expressed simply as xe2x80x9cresistancexe2x80x9d or xe2x80x9cflow resistance.xe2x80x9d